Add examples + explanations (#244)

* expand examples

- show setting image data + add explanation of `ioff` and `Output`
- update github link
- mention display(fig) for a static embed
- remove stale example and add comment to main example

* link to example notebook from readme

Author: ianhi

README.md

@@ -21,6 +21,7 @@ magic:
 ```
 
 ## Example
+See the [example notebook](https://github.com/matplotlib/ipympl/blob/master/examples/ipympl.ipynb) for more!
 
 ![matplotlib screencast](matplotlib.gif)